This invention relates to positioning systems and more particularly to such systems that operate in conjunction with a controller, a microprocessor, or the like. The invention is described in connection with a microprocessor-controlled printer unit, particularly involving the positioning of forms in the printer unit with high precision.
Considerable progress has been made in recent years in microprocessor-controlled systems, but some difficulty has been encountered in achieving compatibility in the operating times, that is, cycle times of the various elements making up such a system. A representative system of this nature may include a microprocessor for controlling operations, for sensing conditions in the system, analyzing such conditions, and providing control signals based on such analysis to the system elements. A printer unit incorporates various assemblies of a more or less electromechanical nature. Examples of this are forms feed assemblies, print assemblies, ribbon drive assemblies and the like. Microprocessors available at this time may have cycle times in the range of 0.2 microseconds to 10 microseconds, for example. Cycle times of the mechanical elements making up a system of this nature are measured usually in milliseconds, rather than microseconds. However, since the microprocessor has so many functions assigned to it during operation of the system, it may be able to devote only a very small amount of its operating cycle time to checking the status of the electromechanical elements or other portions of the system, and it is desirable that a balance be reached between the operating capacity of the microprocessor and the requirements for maintaining close control over all system elements. Thus, it may be desirable to have an arrangement for a system of this type wherein the microprocessor checks the condition of various system elements only on a periodic basis. That is, it is desirable from the standpoint of efficiency that as little time as possible be set aside for checking the system elements. On the other hand, when high quality printing is required, it is essential that positional information, such as that provided from an emitter, be analyzed and acted upon often enough to insure the desired degree of accuracy and quality.